U.S. patent application number 10/722790 was filed with the patent office on 2005-05-26 for aromatics alkylation process.
Invention is credited to Nanda, Vijay.
Application Number | 20050113617 10/722790 |
Document ID | / |
Family ID | 34592073 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050113617 |
Kind Code |
A1 |
Nanda, Vijay |
May 26, 2005 |
Aromatics alkylation process
Abstract
The invention relates to a process for producing alkylated
aromatics, preferably ethylbenzene, in a multiple bed reactor in
which at least two catalysts, each comprising a molecular sieve,
are used in sequential beds. The first alkylation catalyst is
selected to have a higher activity or alpha value than the
subsequent alkylation catalyst.
Inventors: |
Nanda, Vijay; (Houston,
TX) |
Correspondence
Address: |
EXXONMOBIL CHEMICAL COMPANY
5200 BAYWAY DRIVE
P.O. BOX 2149
BAYTOWN
TX
77522-2149
US
|
Family ID: |
34592073 |
Appl. No.: |
10/722790 |
Filed: |
November 25, 2003 |
Current U.S.
Class: |
585/467 |
Current CPC
Class: |
B01J 37/0009 20130101;
B01J 2229/42 20130101; C07C 2/66 20130101; B01J 29/40 20130101;
C07C 2/66 20130101; C07C 15/073 20130101 |
Class at
Publication: |
585/467 |
International
Class: |
C07C 002/68 |
Claims
We claim:
1. A process for alkylating an aromatic hydrocarbon reactant with
an alkylating agent to produce an alkylated aromatic product, said
process comprising: (a) introducing said aromatic hydrocarbon
reactant and said alkylating agent into a reactor unit containing a
plurality of sequentially arranged beds comprised of a first bed
containing a first catalyst effective for alkylating said aromatic
hydrocarbon reactant and a second bed downstream from said first
bed and containing a second catalyst effective for alkylating said
aromatic hydrocarbon reactant and having less catalytic activity
than said first catalyst; (b) alkylating in said first bed under
alkylation conditions said aromatic hydrocarbon reactant with said
alkylating agent to form a first effluent comprising a
mono-alkylaromatic compound, an unreacted portion of the aromatic
hydrocarbon reactant, and polyalkylated aromatic compounds, (c)
alkylating in said second bed under alkylation conditions at least
a portion of said unreacted aromatic hydrocarbon reactant present
in said effluent with said alkylating agent to form a product
effluent, and d) removing said product effluent from said reactor
unit, said product effluent comprising a mono-alkylaromatic
compound, an unreacted portion of the aromatic hydrocarbon
reactant, and polyalkylated aromatic compounds.
2. The process of claim 1, wherein said alkylation conditions
within the reaction zone comprise temperature and pressure
conditions at which the aromatic hydrocarbon reactant is in a vapor
phase.
3. The process of claim 1, wherein the molar ratio of the aromatic
hydrocarbon reactant to the alkylating agent is from about 5 to
about 25.
4. The process of claim 1, wherein the aging rate of the staged
combination of the first and second catalysts is less than the
aging rate of either catalyst individually.
5. The process of claim 1, wherein the first catalyst has an alpha
value greater than the alpha value of the second catalyst.
6. The process of claim 1, wherein the first catalyst has an alpha
value from about 60 to about 200 and the second catalyst has an
alpha value from about 20 to about 100.
7. The process of claim 1, wherein the reactor unit comprises from
4 to 8 catalyst beds.
8. The process of claim 1, wherein the first and second catalysts
each comprise the same molecular sieve.
9. The process of claim 1, wherein the first and second catalysts
each has a crystal size of less than one micron.
10. The process of claim 1, wherein the first catalyst comprises a
molecular sieve and a silica binder and the second catalyst
comprises a molecular sieve and an alumina binder.
11. The process of claim 1, wherein the aromatic hydrocarbon
reactant comprises benzene and the alkylating agent comprises
ethylene.
12. The process of claim 11, wherein at least 65% of the total
benzene introduced to the reactor unit is introduced in the first
bed of the reactor.
13. The process of claim 1, wherein the first catalyst is at least
10% more active than the second catalyst for alkylation of the
aromatic hydrocarbon reactant at the operating conditions of the
first bed.
14. The process of claim 13, wherein the first catalyst is at least
25% more active than the second catalyst for alkylation of the
aromatic hydrocarbon reactant at the operating conditions of the
first bed.
15. The process of claim 14, wherein the first catalyst is at least
50% more active than the second catalyst for alkylation of the
aromatic hydrocarbon reactant at the operating conditions of the
first bed.
16. The process of claim 15, wherein the first catalyst is at least
100% more active than the second catalyst for alkylation of the
aromatic hydrocarbon reactant at the operating conditions of the
first bed.
17. A process for the vapor-phase ethylation of benzene comprising:
a) providing a multi-stage alkylation reaction zone having a
plurality of series-connected catalyst beds, at least one of the
series-connected catalyst beds containing a first alkylation
catalyst comprising a zeolite and at least one subsequent catalyst
bed containing a second alkylation catalyst comprising a zeolite,
the first alkylation catalyst being more active for the ethylation
of benzene than the second alkylation catalyst, b) introducing
benzene and ethylene into the multistage alkylation reaction zone;
c) operating the multistage alkylation reaction zone at temperature
and pressure conditions in which the benzene is in a vapor phase to
cause vapor-phase ethylation of the benzene in the presence of the
first and second alkylation catalysts to produce an alkylation
product comprising a mixture of ethylbenzene and polyalkylated
aromatic components; and d) withdrawing the alkylation product from
the multistage alkylation reaction zone.
18. The process of claim 17, wherein the feedstock has a
benzene/ethylene molar ratio from about 5 to about 25.
19. The process of claim 17, wherein the zeolite in the first
catalyst has a silica/alumina ratio from about 5 to about 200.
20. The process of claim 17, wherein the zeolite in the second
catalyst has a silica/alumina ratio from about 5 to about 200.
21. The process of claim 17, wherein the multistage alkylation
reaction zone comprises 4 to 8 catalyst beds.
22. The process of claim 17, wherein the zeolite of the first and
second alkylation catalysts each has a crystal size of less than
one micron.
23. The process of claim 17, wherein the first alkylation catalyst
is at least 25% more active than the second alkylation catalyst for
the ethylation of benzene at the operating conditions of the first
bed of the reaction zone.
24. The process of claim 23, wherein the first alkylation catalyst
is at least 50% more active than the second alkylation catalyst for
the ethylation of benzene at the operating conditions of the first
bed of the reaction zone.
25. A process for the vapor-phase reaction of ethylene with
benzene, the process comprising: a) introducing benzene and
ethylene, in a molar ratio of benzene to ethylene from about 5 to
about 25 into a multi-stage alkylation reaction zone having a
plurality of series-connected catalyst beds, at least one catalyst
bed containing a first alkylation catalyst comprising a molecular
sieve bound with silica binder and having an alpha value from about
60 to about 200 and at least one subsequent catalyst bed containing
a second alkylation catalyst with an alpha value from about 10 to
about 60; b) operating each stage of the alkylation multistage
reaction zone at temperature and pressure conditions in which the
benzene is in a vapor phase to produce an alkylation product
comprising a mixture of ethylbenzene and polyalkylated aromatic
components; c) withdrawing the alkylation product from the
multistage alkylation reaction zone; d) separating the
polyalkylated aromatic components from the alkylation product; and
e) supplying at least a portion of the polyalkylated aromatic
component along with benzene to a transalkylation reaction zone
operated in the vapor or liquid phase under temperature and
pressure conditions sufficient to cause transalkylation of the
polyalkylated aromatic fraction to produce a transalkylation
product having an enhanced ethylbenzene content and a reduced
polyalkylated aromatic components content.
26. The process of claim 25, wherein the reaction zone comprises
from 4 to 8 catalyst beds.
27. A process for the vapor-phase reaction of ethylene with
benzene, the process comprising: a) introducing benzene and
ethylene, in a molar ratio of benzene to ethylene from about 5 to
about 25 into a multi-stage alkylation reaction zone having a
plurality of series-connected catalyst beds, at least one catalyst
bed containing a first alkylation catalyst comprising a molecular
sieve bound with silica binder and having an alpha value from about
60 to about 200 and at least one subsequent catalyst bed containing
a second alkylation catalyst with an alpha value from about 10 to
about 60; b) operating each stage of the alkylation multistage
reaction zone at temperature and pressure conditions at which the
benzene is in a vapor phase to produce an alkylation product
comprising a mixture of ethylbenzene and polyalkylated aromatic
components; c) withdrawing the alkylation product from the
multistage alkylation reaction zone; d) separating the
polyalkylated aromatic components from the alkylation product; and
e) supplying at least a portion of the polyalkylated aromatic
component to the alkylation reaction zone of step (a) to cause
transalkylation of the polyalkylated aromatic fraction to produce a
transalkylation product having an enhanced ethylbenzene content and
a reduced polyalkylated aromatic components content.
28. The process of claim 27, wherein the reaction zone comprises
from 4 to 8 catalyst beds.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for improving the
efficiency and reducing certain byproducts in alkylation of
aromatic compounds to produce mono-alkylaromatic compounds. In
particular, vapor phase alkylation of benzene to produce
ethylbenzene can be accomplished with increased ethylbenzene purity
and reduced ethylene and benzene loss to byproduct formation.
Alternatively, the capacity of an existing process can be increased
while maintaining product specifications.
BACKGROUND OF THE INVENTION
[0002] A variety of processes for converting aromatics in the
presence of molecular sieve catalysts are known in the chemical
processing industry. Aromatic conversion reactions include
alkylation and transalkylation to produce alkylaromatics such as
ethylbenzene (EB), ethyltoluene, cumene and higher aromatics. An
alkylation reactor which produces a mixture of mono- and
poly-alkylaromatic compounds may be linked in some way with a
transalkylation reactor to maximize the net production of
mono-alkylaromatic compounds. Such alkylation and transalkylation
conversion processes can be carried out in the liquid phase, in the
vapor phase, or under conditions in which both liquid and vapor
phases are present. The preferred catalysts and the byproduct
formation differ with the severity of reaction conditions and the
phase conditions in which the reaction is carried out.
[0003] In efforts to improve commercial alkylation operations,
emphasis is placed not only on the conversion efficiency of the
catalyst but also on the selectivity of the catalyst, including
reduced production of certain byproducts. For example, in the
manufacture of ethylbenzene, ethylene and benzene are introduced
into an alkylation reactor in the presence of various catalysts.
Some of the byproducts include diethylbenzenes, xylenes,
propylbenzene, cumene, butylbenzene, and other components referred
to collectively as heavies. Production of unwanted byproducts
increases feedstock usage as well as the cost of separating such
unwanted byproducts. Byproducts which are not removed can
materially impact the efficiency of downstream operations, such as
the dehydrogenation of EB to form styrene monomer.
[0004] It has been shown that zeolites like ZSM-5 show high
activity and selectivity for vapor phase alkylation of benzene with
ethylene and that catalysts of this type in the acid form remain
active for unusually long periods between regenerations. Discussion
of acid zeolite ZSM-5 for vapor phase alkylation is provided in
U.S. Pat. No. 3,751,506, which is herein fully incorporated by
reference and which describes control of the exothermic heat of
reaction by conducting the reaction in a series of reactors with
intermediate cooling and addition of ethylene between stages.
[0005] Another process for vapor phase alkylation is described in
U.S. Pat. No. 4,107,224, which is herein fully incorporated by
reference. Benzene and dilute ethylene are reacted in vapor phase
over a solid porous catalyst selected from ZSM-5, ZSM-11, ZSM-12,
ZSM-35, ZSM-38, and other similar materials in a series of reaction
zones with intermediate injection of cold reactants and diluent to
control temperature.
[0006] U.S. Pat. No. 6,090,991, which is herein fully incorporated
by reference, describes vapor phase ethylbenzene production in
which a feedstock containing benzene and ethylene is applied to an
alkylation reaction zone having at least one catalyst bed
containing a monoclinic silicalite catalyst having a weak acid site
concentration of less than 50 micromoles per gram.
[0007] U.S. Pat. No. 6,057,485, which is herein fully incorporated
by reference, describes vapor phase ethylbenzene production by
alkylation over a split load of monoclinic silicalite alkylation
catalysts having different silica/alumina ratios. A feedstock
containing benzene and ethylene is applied to a multi-stage
alkylation reaction zone having a plurality of series-connected
catalyst beds. At least one catalyst bed contains a first
monoclinic silicalite catalyst having a silica/alumina ratio of at
least 275. At least one other catalyst bed contains a second
monoclinic silicalite catalyst having a silica/alumina ratio of
less than about 275.
[0008] U.S. Pat. No. 5,998,687, which is herein fully incorporated
by reference, describes ethylbenzene production by alkylation over
a stacked reactor loaded with zeolite beta followed by zeolite Y to
reduce overall flux oil production.
[0009] A disadvantage of vapor phase alkylation reactions is the
formation of polyalkylated byproducts. While the art currently
provides for various transalkylation processes to handle some of
the alkylation byproducts such as diethylbenzene, it would be
desirable to reduce the production of byproducts, especially
byproducts that are not easily handled in an
alkylation/transalkylation process. It would also be desirable to
reduce the quantity of reactants consumed in production of
byproducts
[0010] Recently, catalysts have been developed which allow the
alkylation reactions to be carried out in the liquid phase
alkylation at relatively mild reaction conditions. The reduced
temperature associated with operating in the liquid phase allows
for a significant reduction in undesirable by-products.
[0011] In existing facilities designed for vapor phase reactions,
it can be cost-prohibitive to retrofit for a liquid phase operation
unless a substantial increase in production capacity is required.
Improved catalysts allowing lower temperature operation in such
vapor phase facilities are highly desirable.
SUMMARY OF THE INVENTION
[0012] In one embodiment, this invention is a process for
alkylating an aromatic hydrocarbon reactant with an alkylating
agent to produce an alkylated aromatic product, said process
comprising:
[0013] (a) introducing said aromatic hydrocarbon reactant and said
alkylating agent into a reactor unit containing a plurality of
sequentially arranged beds comprised of a first bed containing a
first catalyst effective for alkylating said aromatic hydrocarbon
reactant and a second bed downstream from said first bed and
containing a second catalyst effective for alkylating said aromatic
hydrocarbon reactant and having less catalytic activity than said
first catalyst;
[0014] (b) alkylating in said first bed under alkylation conditions
said aromatic hydrocarbon reactant with said alkylating agent to
form a first effluent comprising a mono-alkylaromatic compound, an
unreacted portion of the aromatic hydrocarbon reactant, and
polyalkylated aromatic compounds,
[0015] (c) alkylating in said second bed under alkylation
conditions at least a portion of said unreacted aromatic
hydrocarbon reactant present in said effluent with said alkylating
agent to form a product effluent, and
[0016] d) removing said product effluent from said reactor unit,
said product effluent comprising a mono-alkylaromatic compound, an
unreacted portion of the aromatic hydrocarbon reactant, and
polyalkylated aromatic compounds.
[0017] In another embodiment, this invention can be a process for
the vapor-phase ethylation of benzene comprising
[0018] a) providing a multi-stage alkylation reaction zone having a
plurality of series-connected catalyst beds, at least one of the
series-connected catalyst beds containing a first alkylation
catalyst comprising a zeolite and at least one subsequent catalyst
bed containing a second alkylation catalyst comprising a zeolite,
the first alkylation catalyst being more active for the ethylation
of benzene than the second alkylation catalyst,
[0019] b) introducing a feedstock of benzene and ethylene into the
multistage alkylation reaction zone;
[0020] c) operating the multistage alkylation reaction zone at
temperature and pressure conditions in which the benzene is in a
vapor phase to cause vapor-phase ethylation of the benzene in the
presence of the first and second alkylation catalysts to produce an
alkylation-product comprising a mixture of ethylbenzene and
polyalkylated aromatic components; and
[0021] d) withdrawing the alkylation product from the multistage
alkylation reaction zone.
[0022] In yet another embodiment, this invention can be either of
the processes above with the additional steps of separating the
polyalkylated aromatic components from the alkylation product and
supplying at least a portion of the polyalkylated aromatic
component along with benzene to a transalkylation reaction zone
operated in the vapor or liquid phase under temperature and
pressure conditions sufficient to cause transalkylation of the
polyalkylated aromatic fraction to produce a transalkylation
product having an enhanced ethylbenzene content and a reduced
polyalkylated aromatic components content.
[0023] In a further alternative embodiment, the invention can be
any of the processes above, further including the steps of
separating the polyalkylated aromatic components from the
alkylation product; and supplying at least a portion of the
polyalkylated aromatic component to the alkylation reaction zone to
cause transalkylation of the polyalkylated aromatic fraction to
produce a transalkylation product having an enhanced ethylbenzene
content and a reduced polyalkylated aromatic components
content.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows the general configuration of a reactor
containing four catalyst beds.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Introduction
[0026] Aromatics alkylation reactions are highly exothermic, and
many reaction schemes have been developed to control temperature
rise through the reactor in an effort to minimize byproduct
formation. One such solution has been the interstage introduction
of lower temperature aromatic reactant feed streams to both act as
a reactant and a to reduce the temperature by producing a quenching
effect. In most current vapor phase aromatics alkylation reaction
systems, multiple beds of the same catalyst are used sequentially
for alkylaromatic production. For example, in a typical
ethylbenzene reactor which operates with between four and eight
catalyst beds, only about 50 to 65% of the benzene feed can be
directed towards the top bed (reactor inlet). The remaining benzene
is added between the catalyst beds as a heat sink for temperature
control (quenching) purposes, since each bed operates optimally at
essentially the same inlet temperature. This mode of operation
generally causes the lowest and highest benzene to ethylene ratios
to occur in the top and bottom beds respectively. The lower benzene
flow in bed 1 of the reactor leads to higher by-products formation
due to reduced localized benzene to ethylene ratio and higher
temperature rise across the catalyst bed.
[0027] This invention provides for an improved process for the
production of alkylaromatics by contacting the reactants in a
reaction zone maintained under such conditions that the reaction
occurs in the vapor phase and in the presence of at least two
catalysts exhibiting different activity. This allows the reaction
zone, comprising a series of catalyst beds, to operate at more
varied temperatures and can reduce or eliminate the need for
quenching or otherwise cooling the effluent from each stage.
[0028] Arranging the catalyst in the alkylation reactor such that
the highest activity catalyst is in one or more upper bed(s) and
the lowest activity catalyst is in one or more later bed(s) allows
the beds to operate at more varied inlet temperatures. It would now
be preferable to have a rising temperature profile as the aromatic
compound, for example benzene, and the alkylating agent, for
example ethylene, flow through the reactor.
[0029] FIG. 1 shows a simplified four-bed reactor, in which the
feed to the first catalyst bed 1 is a mixture of the aromatic
reactant and the alkylating agent. Additional alkylating agent 2
and optionally additional aromatic reactant 8 are combined with the
effluent from the first bed and introduced to the second catalyst
bed. Again, additional alkylating agent 4 and optionally additional
aromatic reactant 10 are combined with the effluent from the second
bed and introduced to the third catalyst bed. The same steps are
repeated with additional alkylating agent 6 and optionally
additional aromatic reactant 12 being combined with the effluent
from the third catalyst bed and introduced to the fourth catalyst
bed. The effluent from the fourth catalyst bed 14 comprises a
mono-alkylated aromatic compound, unreacted aromatic reactant, and
poly-alkylated aromatic compounds. In the processes of the
invention, at least the first bed, and optionally up to the first
three beds contain a higher activity alkylation catalyst, and the
input of aromatic reactant is shifted from inlets 8, 10, and/or 12
to inlet 1.
[0030] In one embodiment where the aromatic hydrocarbon reactant is
benzene and the alkylating agent is ethylene, this catalyst
arrangement would allow more of the benzene, preferably greater
than 60 wt. % of the total, more preferably greater than 80 wt.%,
and most preferably 100%, to be directed toward the top (first)
bed, resulting in an increased localized benzene to ethylene ratio
and reduced temperature rise across the upper catalyst bed in a
downflow arrangement. This improvement would result in both
improved process yield and reduced byproduct formation,
particularly reduced formation of byproducts not easily
transalkylated to form ethylbenzene.
[0031] In one embodiment of the present invention, highest activity
catalyst is loaded into the top (first) bed(s) and lowest activity
catalyst is loaded into the bottom bed(s). This allows the top bed
to operate at the lowest inlet temperature and the catalyst
temperature increases progressively as the reactants move towards
the lower beds. This catalyst arrangement requires little or no
quench benzene to be added interstage between the beds for
temperature control purposes. The quench benzene can be diverted
towards the top catalyst bed, thereby increasing both the overall
(benzene and ethylene) weight hourly space velocity (WHSV) and the
localized benzene to ethylene ratio through the upper catalyst
beds. This benzene shift provides a severity compensation for the
higher activity catalyst beds and also reduces the temperature
increase across these beds due to a lower ethylene concentration.
Product purity is improved by operating at a higher localized
benzene to ethylene ratio, higher overall WHSV, and lower
temperatures both at the inlet and within the catalyst beds.
Reduced decline in catalyst activity relative to throughput is an
additional unexpected benefit of this invention.
[0032] In an alternative embodiment, staging a higher activity
catalyst in a first catalyst bed with a lower activity catalyst in
a second catalyst bed can also be used to increase the capacity of
a process configuration without increasing the overall aromatic
reactant circulation and the associated increased production of
undesirable byproducts.
[0033] Catalysts suitable for vapor phase alkylation of aromatics
include a variety of molecular sieves, particularly aluminosilicate
zeolites, which are classified by framework type and described by
the Structure Commission of the International Zeolite Association
according to the rules of the IUPAC Commission on Zeolite
Nomenclature. A framework-type describes the topology and
connectivity of the tetrahedrally coordinated atoms constituting
the framework and makes an abstraction of the specific properties
for those materials. Molecular sieves for which a structure has
been established are assigned a three letter code and are described
in the Atlas of Zeolite Framework Types, 5th edition, Elsevier,
London, England (2001), which is herein fully incorporated by
reference.
[0034] Other molecular sieves include those described in R.
Szostak, Handbook of molecular Sieves, Van Nostrand Reinhold, New
York, N.Y. (1992), which is herein fully incorporated by
reference.
[0035] Molecular sieves preferred for use in the catalysts of this
invention are those having intermediate pore sizes, preferably
having a pore dimension from about 5 Angstroms to about 7
Angstroms. Examples of suitable molecular sieve materials for use
in the alkylation catalysts of this invention include, but are not
limited to, ZSM-5, described in U.S. Pat. No. 3,702,886; ZSM-11,
described in U.S. Pat. No. 3,709,979; ZSM-12, described in U.S.
Pat. No. 3,832,449; ZSM-35, described in U.S. Pat. No. 4,016,245;
and ZSM-38, described in U.S. Pat. No. 4,046,859.
[0036] In practicing a particular desired chemical conversion
process, it may be useful to incorporate any of the above-described
crystalline zeolites with a matrix or binder comprising another
material resistant to the temperature and other conditions employed
in the process.
[0037] Useful matrix materials include both synthetic and naturally
occurring substances, as well as inorganic materials such as clay,
silica and/or metal oxides. The latter may be either naturally
occurring or in the form of gelatinous precipitates or gels
including mixtures of silica and metal oxides. Naturally occurring
clays which can be composited with the zeolite include those of the
montmorillonite and kaolin families, which families include the
sub-bentonites and the kaolins commonly known as Dixie,
McNamee-Georgia and Florida clays or others in which the main
mineral constituent is halloysite, kaolinite, dickite, nacrite, or
anauxite. Such clays can be used in the raw state as originally
mined or initially subjected to calcination, acid treatment, or
chemical modification.
[0038] In addition to the foregoing materials, the zeolites
employed herein may be composited with a porous matrix material,
such as alumina, silica-alumina, silica-magnesia, silica-zirconia,
silica-thoria, silica-beryllia, and silica-titania, as well as
ternary compositions, such as silica-alumina-thoria,
silica-alumina-zirconia, silica-alumina-magnesia and
silica-magnesia-zirconia. The matrix may be in the form of a cogel.
The relative proportions of zeolite component and inorganic oxide
gel matrix, on an anhydrous basis, may vary widely with the zeolite
content ranging from between about 1 to about 99 percent by weight
and more usually in the range of about 5 to about 80 percent by
weight of the dry composite.
[0039] Activity of a catalyst can be impacted by various factors
including the synthesis method, silica/alumina ratio, selection of
binder, shape of the extruded particles, steaming, and other
treatments. One measurement of relative activity of catalysts for
certain kinds of reactions is the alpha value. Catalytic activity
of zeolites, such as ZSM-5, is often reported using alpha value,
which compares the catalytic cracking activity of the catalyst
(rate of normal hexane conversion per volume of catalyst per unit
time) with the activity of a standard silica-alumina cracking
catalyst. The alpha test is described in U.S. Pat. No. 3,354,078;
in the Journal of Catalysis, Vol. 4, p. 527 (1965); Vol. 6, p. 278
(1966); and Vol. 61, p. 395 (1980). The experimental conditions of
the test used herein include a constant temperature of 538.degree.
C. and a variable flow rate as described in detail in the Journal
of Catalysis, Vol. 61, p. 395.
[0040] For aluminosilicate zeolites such as ZSM-5, the alpha value
generally decreases with increasing silica/alumina ratio in the
synthesized zeolite. Preferred silica/alumina ratios for the
catalysts of the present invention are less than 200: 1, more
preferably less than 100:1, and most preferably from about 12:1 to
about 80:1. Other variables which have been found to impact the
activity of the zeolite are the crystal size and the selection of
binder material. The alpha value of an as-synthesized zeolite or a
catalyst composition can be reduced for a specific application
through a variety of treatment methods.
[0041] Alpha value is a better indicator of catalyst activity for
some reactions than for others. For the purposes of this invention,
catalysts would be selected for a particular alkylation reaction
based on their overall suitability for that reaction. An
alternative measurement of catalyst activity suitable for use in
this invention would be a comparison of conversion between
catalysts at a given base set of operating conditions for the
reaction to be conducted. Appropriate comparisons can be made based
on conversion rates at the least severe operating conditions
appropriate for either of the catalysts being compared. The
catalyst with higher conversion at the test conditions would be the
more active catalyst and would therefore be selected for the
initial bed(s) of the reactor.
[0042] Preferably the catalyst used in the first bed(s) of the
reactor would be at least 10% more active than the catalyst used in
a subsequent bed, based on a comparison of conversion rates at the
operating conditions of the first bed of the reactor. Even more
preferably, the catalyst used in the first bed(s) would be at least
20% more active for the given reaction than the catalyst used in a
subsequent bed. Catalyst selections with 25%, 50%, 75%, 100%, and
greater than 100% difference in activity would be useful in this
invention.
[0043] In one embodiment, the same zeolite would be used for the
catalyst in each of the beds, but that zeolite would be treated so
as to alter its activity. For example, different binders could be
used for formulating the catalyst used in the different beds.
Silica used as a binder has been found to result in a higher
activity catalyst for aromatics alkylation than alumina. Another
example would be steaming or otherwise reducing the activity from
the "as-synthesized" level to two different levels, and using the
higher activity catalyst for the initial bed(s) in the reactor
followed by one or more beds containing the lower activity
catalyst. For example, an as-synthesized ZSM-5 may have a very high
alpha value, but two batches of the same zeolite could be treated
to reduce the respective alpha values such that the alpha value of
the first is approximately double the alpha value of the
second.
[0044] Alternatively, two different zeolites could be used so long
as they were selected to place the higher activity formulated
catalyst in the initial bed(s) of the reactor.
[0045] It will be recognized that the surprising results herein
originate from the concept of staging the catalysts by relative
activity levels and that this effect will be obtained with one or
more beds of higher activity catalyst followed by one or more beds
of lower activity catalyst regardless of the actual number of beds
of each catalyst or in the reactor as a whole. Although the
examples contained herein refer to a first and second alkylation
catalyst for ease of description, it will be recognized by those
skilled in the art that this invention applies equally to the use
of more than two levels of catalyst activity.
[0046] A catalyst suitable for use as the first alkylation catalyst
of the invention would be a molecular sieve suitable for use in
aromatics alkylation processes, preferably a molecular sieve bound
with silica. The first alkylation catalyst would preferably be
treated to reduce the alpha number from an as-synthesized alpha
value but would generally still have a relatively high alpha
number.
[0047] An example of one catalyst suitable for use as the first
catalyst would be a silica bound ZSM-5 zeolite with relatively high
alpha activity compared to that generally preferred for the
specific operating conditions.
[0048] A preferred first catalyst would be approximately 65% ZSM-5
bound with approximately 35% SiO2. Preferably the ZSM-5 is in the
form of small crystals, preferably less than about 0.08 micron in
diameter. The SiO2/Al2O3 ratio of the ZSM-5 would be less than
about 200:1, preferably from about 5:1 to about 200:1, more
preferably from about 20:1 to about 100:1, and most preferably from
about 50:1 to about 75:1. The SiO2 binder is preferably comprised
of between 10 and 90% colloidal silica sol such as Ludox HS-40,
more preferably about 50% colloidal silica sol, and between 10 and
90% precipitated silica such as Ultrasil, more preferably about 50%
precipitated silica. The catalyst would preferably be prepared by
extruding the ZSM-5 with the colloidal silica sol and precipitated
silica (water and NaOH can be added to facilitate the extrusion)
and drying the extrudate. A preferred shape is {fraction
(1/16)}-inch cylindrical extrudates.
[0049] In one preferred embodiment, the dried extrudate is then
humidified with a steam/air mixture and is exchanged with 1N
ammonium nitrate to remove sodium. The exchange is followed by a
water wash with deionized water. The exchange/wash procedure is
preferably repeated. The catalyst would then be dried, calcined to
about 600 to 1200.degree. F. (about 315 to 650.degree. C.),
preferably about 1000.degree. F. (about 538.degree. C.), preferably
in nitrogen followed by a mixture of air and nitrogen. The first
catalyst would then be steamed to reduce the alpha activity to an
alpha value from about 60 to about 200, preferably from about 70 to
about 100.
[0050] A suitable second catalyst could comprise the same ZSM-5
zeolite, preferably prepared by extruding the ZSM-5 with alumina
(water can be added to facilitate the extrusion) to {fraction
(1/16)}-inch cylindrical extrudates, drying the extrudate,
calcining the dried extrudate to about 600 to 1200.degree. F.
(about 315 to 650.degree. C.), preferably about 1000.degree. F.
(about 538.degree. C.), in nitrogen followed by a mixture of air
and nitrogen. The second catalyst could then be steamed to reduce
the alpha activity to a value less than that of the first catalyst,
preferably less than about 60, preferably from about 35 to about
55.
[0051] While the selection of different binder materials and
steaming to different endpoints was described above, it will be
recognized by those of ordinary skill in the art that any selection
or treatment method suitable for staging the relative activity of
aromatics alkylation catalysts will fall within the scope of this
invention.
[0052] One embodiment of this invention includes reduction and/or
elimination of interstage benzene addition. The use of a higher
activity catalyst in the first bed(s) allows for conversion using a
lower temperature feed. This would then allow reduction of the
interstage quench, further reducing the temperature increase in the
first bed(s). Both the reduction in temperature and the increased
B/E ratio reduce the production of unwanted byproducts.
Alternatively, it may be possible to reduce the overall B/E ratio
to the reactor as a whole, thus reducing operating costs associated
with recycling aromatics such as benzene back to the process.
[0053] In another embodiment, this invention can be a process for
the vapor-phase reaction of ethylene with benzene, in a molar ratio
of benzene to ethylene from about 5 to about 25, preferably 6 to 7,
in a multi-stage alkylation reaction zone having a plurality of
series-connected catalyst beds, preferably from 4 to 8 beds. The
reaction zone would comprise at least one catalyst bed containing a
first alkylation catalyst comprising a molecular sieve, preferably
bound with silica binder, and having an alpha value from about 60
to about 200, preferably from about 70 to about 100, and at least
one subsequent catalyst bed containing a second alkylation catalyst
with an alpha value from about 10 to about 60. The reaction zone
would be operated at alkylation conditions including temperature
and pressure conditions in which the benzene is in a vapor phase to
produce an alkylation product comprising a mixture of ethylbenzene
and polyalkylated aromatic components. The alkylation product would
be withdrawn from the multistage alkylation reaction zone, the
polyalkylated aromatic components would be separated from the
alkylation product; and at least a portion of the polyalkylated
aromatic component would be supplied along with benzene to a
transalkylation reaction zone operated in the vapor or liquid phase
under temperature and pressure conditions sufficient to cause
transalkylation of the polyalkylated aromatic fraction to produce a
transalkylation product having an enhanced ethylbenzene content and
a reduced polyalkylated aromatic components content.
[0054] A further alternative embodiment would involve alkylation of
the aromatic component as described above, except that at least a
portion of the separated polyalkylated aromatic components would be
recycled to the alkylation reaction zone to cause transalkylation
of the polyalkylated aromatic fraction to produce a product having
an enhanced ethylbenzene content and a reduced polyalkylated
aromatic components content.
EXAMPLES
[0055] In order to provide a better understanding of the present
invention including representative advantages thereof, the
following examples are offered. Examples 1 and 2 will describe the
use and performance of two individual catalyst compositions in
ethylbenzene production. Example 3 will demonstrate the performance
of a reactor using the catalysts of Examples 1 and 2 in sequential
beds, and Example 4 will describe the impact of using the design of
example 3 with increased throughput. Examples 5, 6, and 7 will
provide the results of the individual catalysts in a six-bed
reactor and a simulation of the results expected from the
application of this invention to that reactor.
Example 1 (Comparative)
Single Catalyst
[0056] A catalyst was prepared by extruding ZSM-5, having an
average crystal size less than 0.08 micron and a SiO2/Al2O3 ratio
of approximately 60:1, with alumina (water is added to facilitate
the extrusion) to {fraction (1/16)}-inch cylindrical extrudates
having approximately 35% alumina, drying the extrudate, calcining
the dried extrudate to approximately 1 000.degree. F. (about
540.degree. C.) in nitrogen followed by a mixture of air and
nitrogen. The catalyst was then steamed to reduce the alpha
activity to between 35 and 55.
[0057] This catalyst was loaded into all four beds of a four-bed
reactor as shown in FIG. 1. Ethylene and benzene were introduced
into the reactor with an overall weight ratio of benzene to
ethylene (B/E) of 21.6 and a WHSV of 70.8 hr.sup.-1 based on the
combined throughput of benzene and ethylene. The details of the
percent of total ethylene input at each stage, the percent of total
benzene input at each stage, the inlet temperature at each stage,
the resulting product impurity levels, and the decline in catalyst
activity are shown in Table 1. It is noted that overallethylene
conversion using fresh catalyst is generally in the 99.8 to 99.95
weight % range.
Example 2 (Comparative)
Single Higher Activity Catalyst
[0058] A second catalyst was prepared using the same type of ZSM-5
with approximately 35% silica binder (approximately 50% Ludox
HS-40, a colloidal silica sol, with approximately 50% Ultrasil, a
precipitated silica. The catalyst was prepared by extruding the
ZSM-5 with the Ultrasil and Ludox (water and NaOH were added to
facilitate the extrusion) to {fraction (1/16)}-inch cylindrical
extrudates, drying the extrudate. The dried extrudate was then
humidified with a steam/air mixture and exchanged with 1N ammonium
nitrate to remove sodium. The exchange was followed by a water wash
with deionized water. The exchange/wash procedure was repeated. The
catalyst was then dried, calcined to approximately 1000.degree. F.
(about 540.degree. C.) in nitrogen followed by a mixture of air and
nitrogen. The catalyst was then steamed to reduce the alpha
activity to between 70 and 100.
[0059] This catalyst was loaded into all four beds of a four-bed
reactor as shown in FIG. 1. Ethylene and benzene were introduced
into the reactor with an overall weight ratio of benzene to
ethylene (B/E) of 22.0 and a WHSV of 71.9 hr.sup.-1 based on the
combined throughput of benzene and ethylene. For Example 2, the
ethylene and benzene feed rate are shown as a percentage of the
feed rates in Example 1. Details of the percent of total ethylene
input at each stage, the percent of total benzene input at each
stage, the inlet temperature at each stage, the resulting product
impurity levels, and the decline in catalyst activity are shown in
Table 1.
[0060] It is noted that Example 2, using the higher activity
catalyst, reflects lower concentrations of xylenes, DEB, and
heavies in the ethylbenzene product.
Example 3
Staged Catalyst Beds with Constant Throughput
[0061] For the purpose of Example 3, the catalyst of Example 2 was
loaded into the first 2 beds of the reactor, and the catalyst of
Example 1 was loaded into the subsequent 2 beds of the reactor.
Again, throughput was held roughly constant with the feed rates
again shown as percentages of the feed rates represented by Example
1. The results of this configuration are shown in Table 1. It is
noted that, surprisingly, the resulting impurities are
significantly lower than those of either catalyst alone.
Example 4
Staged Catalyst Beds with Increased Throughput
[0062] In Example 4, the reactor was loaded with catalyst as in
Example 3, but throughput of both ethylene and benzene were
increased by 17.2% and 3.9% respectively as compared to Example 1.
Surprisingly, this increase in throughput did not result in
significantly higher impurities or a higher decline in catalyst
activity than those shown in Example 1.
[0063] The surprising benefits of this invention can either be
utilized to improve product purity or to increase reactor capacity.
A 10 to 15% increase in reactor capacity has significant economic
benefits. Another surprising result is that the catalyst aging
rate, expressed in terms of decline in % conversion per month is
lower for the combination of catalysts shown in Example 3. In
Example 4, the aging rate was higher, but even with significantly
higher throughput, the aging rate was not as high as the weighted
average of the rates experienced by either catalyst alone.
1TABLE 1 Alkylation of Benzene in a 4-Bed Reactor Example 1 2 3 4
Ethylene Feed Rate 100.0 99.8 100.6 117.2 Benzene Feed Rate 100.0
101.6 100.6 103.9 WHSV (hr.sup.-1) 70.8 71.9 71.3 74 Overall B/E
(wt.) 21.6 22.0 21.6 19.1 Bed 1 B/E (wt.) 53.2 56.6 76.3 61.3 Bed 1
Ethylene (%) 27.6 27.8 21.8 23.2 Bed 2 Ethylene (%) 27.2 28.7 27.0
26.2 Bed 3 Ethylene (%) 27.2 28.7 30.9 27.6 Bed 4 Ethylene (%) 17.9
14.9 20.3 22.9 Bed 1 Benzene (%) 68.0 71.7 77.0 74.5 Bed 2 Benzene
(%) 10.9 9.8 9.5 12.6 Bed 3 Benzene (%) 10.9 9.8 7.0 6.8 Bed 4
Benzene (%) 10.2 8.8 6.5 6.2 Bed 1 Inlet (.degree. C.) 404 388 376
371 Bed 2 Inlet (.degree. C.) 390 391 380 376 Bed 3 Inlet (.degree.
C.) 383 393 390 385 Bed 4 Inlet (.degree. C.) 396 396 399 391 p-
& m-Xylene (ppm) 1660 1500 1360 1700 o-Xylene (ppm) 480 420 380
500 DEB/EB (wt. %) 26.65 24.55 21.8 25.6 Heavies (ppm) 3100 2600
2200 2900 Ethylene Conversion 0.018 0.01 0.009 0.012 Decline (wt.
%/mo.)
Examples 5, 6, and 7
[0064] Examples 5 and 6 provide actual data for each of the
catalysts of Examples 1 and 2 respectively when used in a six-bed
reactor. Example 7 provides a hypothetical example of the staged
activity combination of catalysts of this invention when applied to
a six-bed reactor, with three beds of the more active catalyst
followed by three beds of the less active catalyst. The data for
these three examples are presented in Table 2 for comparison.
2TABLE 2 Alkylation of Benzene in a 6-Bed Reactor Example 5 6 7
Ethylene Feed Rate 100.0 100.6 101.7 Benzene Feed Rate 100.0 100.2
101.1 WHSV (hr.sup.-1) 40.0 39.9 40.3 Overall B/E (wt.) 17.3 17.2
17.2 Bed 1 B/E (wt.) 67.5 90.9 105.7 Bed 1 Ethylene (%) 12.6 10.7
10.4 Bed 2 Ethylene (%) 13.8 13.9 13.5 Bed 3 Ethylene (%) 15.5 15.5
16.8 Bed 4 Ethylene (%) 17.3 17.3 18.0 Bed 5 Ethylene (%) 19.4 21.1
20.4 Bed 6 Ethylene (%) 21.3 21.4 21.0 Bed 1 Benzene (%) 49.2 56.6
63.7 Bed 2 Benzene (%) 6.7 5.0 4.7 Bed 3 Benzene (%) 9.0 10.0 6.8
Bed 4 Benzene (%) 10.4 8.0 7.1 Bed 5 Benzene (%) 11.6 10.8 9.1 Bed
6 Benzene (%) 13.0 9.5 8.4 Bed 1 Inlet (.degree. C.) 372 365 354
Bed 2 Inlet (.degree. C.) 378 366 359 Bed 3 Inlet (.degree. C.) 382
371 364 Bed 4 Inlet (.degree. C.) 383 377 369 Bed 5 Inlet (.degree.
C.) 385 380 379 Bed 6 Inlet (.degree. C.) 388 381 388 p- &
m-Xylene (ppm) 410 390 320 o-Xylene (ppm) 110 100 80 DEB/EB (wt. %)
10.5 9.0 8.0 Heavies (ppm) 2300 2000 1650 Ethylene Conversion 0.015
0.008 0.007 Decline (wt. %/mo.)
* * * * *